1. Field of the Invention
The invention relates to a method and apparatus for measuring the concentration of the .sup.129 I.sub.2 isotope in a gas. More specifically the invention relates to the use of a laser to cause the .sup.129 I.sub.2 isotope to produce fluorescence emission from which the concentration of the isotope may be measured while not exciting other iodine istope atoms, such as .sup.127 I and .sup.131 I.